Electrolytic wastewater treatment apparatus

ABSTRACT

A method and apparatus for purifying aqueous effluent streams to reduce chemical oxygen demand thereof, where the method comprises direct oxidation of water-soluble organic material in an electrochemical cell that incorporates stainless steel electrodes, whose stability and lifetime are enhanced by inclusion of circulating metal chips.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of pending U.S. patent application No.09/298,284, filed Apr. 23, 1999 now U.S. Pat. No. 6,274,028 in the namesof Patrick Pei-Chih Hu, Pual Pei-Yung Hu, and Clyde Kuen-Hua Hu.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to a method and apparatus for purifyingaqueous effluent streams to reduce contamination as measured by chemicaloxygen demand, where the method comprises direct oxidation ofwater-soluble organic and oxidizable inorganic substances in anelectrolytic oxidation cell that incorporates stainless steelelectrodes, and wherein the stability and lifetime of the anode areenhanced by incorporation of metal chips.

2. Description of the Related Art

Industrial wastewater streams may be contaminated by various substancesthat render their discharge into waterways or municipal waste treatmentsystems problematic or illegal. Contaminants may be organic or inorganicin nature and are often found in complex combinations.

One widely regulated parameter is “chemical oxygen demand” (COD), ameasure of the quality of wastewater effluent streams prior todischarge. The COD test predicts the oxygen requirement for completeoxidation of oxidizable contaminants present in the effluent; it is usedfor the monitoring and control of discharges, and for assessingtreatment plant performance. Chemical oxygen demand is defined as theamount of oxygen in milligrams per liter (parts-per-million, ppm)required-to oxidize both organic and oxidizable inorganic compounds thatare present in the effluent.

The United States Environmental Protection Agency (USEPA) provides a setof standard methods to determine COD in aqueous effluents:

USEPA Test Method Document Source Chemical Oxygen Demand - 0410.4600/4-79-020 Colorimetric Chemical Oxygen Demand - Semi- 0410.4600/R-93-100 Automated Colorimetric Chemical Oxygen Demand - 0410.3600/4-79-020 Titrimetric, High Level Chemical Oxygen Demand - 0410.2600/4-79-020 Titrimetric, Low Level Chemical Oxygen Demand - 0410.1600/4-79-020 Titrimetric, Mid Level

Acceptable wastewater treatment methods must be cost-effective, andhence a desirable method will be characterized by rapidity ofcontaminant removal, stability of the process over time, low cost ofenergy and consumables, and simplicity of equipment design. In thisview, electrolytic oxidation is a favorable method for reducing theamount of organic compounds and other oxidizable species in an aqueouseffluent to a level that is acceptable for discharge to a treatmentfacility. Electrolytic oxidation has several advantages over chemical orthermal treatment techniques, including ease of operation, simplicity ofdesign, and relatively small equipment space requirements. Electrolysisis also considered to be relatively safe to operate when compared tooxidative treatment techniques which require handling of powerfulchemical oxidants.

The electrolytic treatment of wastewater has been the subject of muchresearch and many patents, e.g., U.S. Pat. No. 4,445,990, “ElectrolyticReactor for Cleaning Wastewater,” issued May 1, 1984; U.S. Pat. No.5,516,972, “Mediated Electrochemical Oxidation of Organic Wastes WithoutElectrode Separators,” issued May 14, 1996; U.S. Pat. No. 5,688,387,“Turbo Electrochemical System,” issued Nov. 18, 1997.

However there remain a number of problems associated with known methodsof lectrolytic oxidation of solutes in wastewaters. An important focusof difficulty is the lack of table, inexpensive anode materials.

In wastewater purification, a high oxygen overvoltage is required at theanode for water-oxidation intermediates to be formed from degradation ofoxidation-resistant organic substances. Most anode materials graduallycorrode during use in electrolytic oxidation, especially in harshchemicals. Corrosion of typical anodes such as platinum, rutheniumoxide, lead dioxide and tin dioxide results in a lack of processstability, is uneconomical, and leads to discharge of unacceptable toxicspecies into the environment. Platinum anodes are the most acceptable oftraditional electrodes, yet in practice the rate of platinum loss fromthe electrode is high enough that a metal recovery system would berequired, adding significantly to the cost and complexity of such anelectrolytic oxidation apparatus and method. Lead dioxide and graphiteelectrodes are not sufficiently stable: modification by tin oxide dopinghas been proposed to increase electrode lifespan, but leads to theaforementioned problem of release of a toxic species.

Furthermore, many anode materials tend to become fouled duringelectrolytic oxidation of various solutes by the formation of anadsorbed layer of residue on the working surface of the anode. Thislowers the effectiveness and useful lifetime of the anode, resulting inlonger treatment times and more frequent equipment-related shutdowns. Ananode that is not subject to a decrease in efficiency due to change inpolarization at the electrode surface is needed in the art.

An additional problem with conventional anode materials is lack ofenergy efficiency when used in electrolytic oxidations. As a result ofsuch deficiencies, the wastewater treatment system requires a relativelylong time and high energy expenditure to achieve desired results, at theelectrical current densities that are typically employed.

The development of suitable electrode materials for wastewater treatmenthas long been an active area of research. Some representative approachesare described in the following patents. U.S. Pat. No. 4,360,417,“Dimensionally Stable High Surface Area Anode Comprising GraphiticCarbon Fibers,” issued Nov. 23, 1982, describes anodes comprisingcarbonaceous fibrous materials with a surface coating of a mixture oftitanium dioxide and ruthenium dioxide. U.S. Pat. No. 4,415,411, “AnodeCoated with β-Lead Dioxide and Method of Producing Same,” issued Nov.15, 1983, describes an anode which comprises various layers of titanium,a platinum-group metal, and a lead dioxide coating. U.S. Pat. No.5,399,247, “Method of Electrolysis Employing a Doped Diamond Anode toOxidize Solutes in Wastewater,” issued Mar. 21, 1995, describes an anodecomprising electrically conductive crystalline doped diamond. Suchelectrodes do not overcome the problems of high cost, contribution oftoxic species to the waste stream, and lack of process stability due tocorrosion or formation of adsorbed layers on the electrode surface.

Electrodes that comprise particulate materials are known. Electrodescomprising electroconductive particulates have been described forcathodic processes such as electroprecipitation or electrowinning, thatis, the recovery of a metal by deposition of the metal from an aqueoussolution, such as a metal-ion-contaminated wastewater or aqueous leachliquors obtained by leaching ore. The metal to be recovered is depositedonto the cathode to a desired thickness, and the cathode is then removedand the metal recovered. Particulate cathodes are described, e.g., inU.S. Pat. No. 4,692,229, “Electrode Chamber Unit for an Electro-ChemicalCell Having a Porous Percolation Electrode,” issued Sept. 8, 1987; U.S.Pat. No. 3,974,049, “Electrochemical Process, issued Aug. 10, 1976; andreferences cited therein. Because the process constraints of thecathodic applications for which these electrodes are designed are quitedifferent, such particulate cathode materials, e.g., graphite, copper,do not have the ability to be used as the anode in an electrolyticoxidation and cannot be operated with high energy-efficiency and in thepresence of oxygen over-voltages, as would be required for an oxidativewastewater purification process.

An organic or organometallic synthesis process using an anode comprisingmetal particulates which are consumed in the synthesis reaction has beendescribed in U.S. Pat. No. 4,828,667, “Electrolytic Cells withContinuously Renewable Sacrificial Electrodes,” issued May 9, 1989. Thispatent describes the electrocarboxylation of 2-acetonaphthone with theaccompanying consumption of the anode. The electrocarboxylation processdisclosed in this reference utilizes small aluminum cylinders which arecontinuously consumed and replenished by a feed device, and involves thefollowing electrochemical reactions:

Anodes designed for such processes are not readily adaptable to use inan electrolytic oxidative wastewater purification process. Further, thealuminum anode in such system would contribute toxic aluminum to thewaste stream and would quickly become passivated by an oxide coating.

There is thus a compelling need for a method and apparatus forelectrolytic oxidation of solutes in liquid solutions, which will avoidor minimize the problems described above. Such a method and apparatuswill desirably have the following features: an anode formed of arelatively inexpensive material and of relatively simple design; ananode whose corrosion does not result in discharge of toxic species; ananode that does not become significantly inefficient through foulingcaused by the formation of an adsorbed layer; an anode that operateswith high energy-efficiency; and an anode whose ongoing corrosion doesnot destabilize the process variables over time.

SUMMARY OF THE INVENTION

The present invention in one aspect relates to an electrolyticpurification method and apparatus for treatment of wastewaters to reducechemical oxygen demand, by oxidation of water-soluble organic and otheroxidizable materials contained therein. The electrolytic purificationsystem of the invention utilizes one or more electrochemical cells. Thecells employ stainless steel electrodes and contain iron chips, whichare mobile and circulate freely as liquid flows through the cell. Theiron chips are in electrical contact with the anode and are preventedfrom making contact with the cathode by a non-conductive butliquid-permeable barrier. The iron chips thus provide a dynamic andfluid electrode surface that is efficient and resistant to performancedegradation.

In the practice of the invention, a voltage, e.g., of 1-20 volts (V), isapplied across the electrodes to generate a desired current, e.g., of2-15 amperes (A). Electrolysis in such a cell reduces COD in typicalwastewaters by oxidizing to CO₂ water-soluble organic and otheroxidizable contaminants.

The invention relates in another aspect to an electrolytic oxidationapparatus, comprising two or more electrochemical cells of theabove-described type, arranged in series for sequential flow ofwastewater therethrough to effect the desired level of COD removal.

In one specific embodiment, the invention relates to an electrolyticoxidation process for purifying a wastewater stream by oxidation ofwater-soluble organic and oxidizable inorganic substances containedtherein, such process including the steps of:

a flowing the wastewater stream into an electrolytic oxidation cell,wherein the cell comprises stainless steel anode and cathode andcontains iron chips, with the chips being in electrical contact with theanode and prevented from making electrical contact with the cathode by anon-electrically-conductive, liquid-permeable barrier;

applying a voltage across the electrodes sufficient to produce a currentof from about 2 to about 20 A.

In one embodiment of the inventive process, the wastewater stream ischaracterized by a conductivity of from about 200 to about 2000 microSiemens per centimeter (μS/cm) and COD of from about 200 to about 2000parts per million by volume (ppm). The electrolytic oxidation cell ispreferably filled to between 80% and 95% of its volumetric capacity withthe iron chips, and the non-electrically-conductive, liquid-permeablebarrier preferably comprises a plastic netting. The wastewater streammay be recirculated through the electrolytic oxidation cell to achievedesired levels of purity.

The inventive process in another aspect may comprise:

flowing the wastewater through one or more additional electrolyticoxidation cells, correspondingly constructed to comprise stainless steelanode and cathode elements and to contain iron chips, in which the chipsbeing in electrical contact with the anode and prevented from makingelectrical contact with the cathode by a non-electrically-conductive,liquid-permeable barrier;

applying a voltage across the across the electrodes of the additionalelectrolytic oxidation cells sufficient to produce a current of fromabout 2 to about 20 A.

The invention in another specific aspect further comprises anelectrolytic oxidation apparatus for purifying a wastewater stream byoxidation of water-soluble organic and oxidizable inorganic substancescontained therein. Such apparatus comprises:

an electrolytic oxidation cell, where the cell comprises stainless steelanode and cathode and contains iron chips, said chips being inelectrical contact with the anode and prevented from making electricalcontact with the cathode by a non-electrically-conductive,liquid-permeable barrier;

means, such as a current source, power supply, generator, turbine, powercable or other electrical power elements, for applying a voltage acrossthe stainless steel anode and cathode sufficient to produce electrolyticoxidation conditions for oxidation of organic and oxidizable inorganicsubstances in the wastewater;

means, e.g., including flow circuitry elements such as piping, conduits,flow channels, connecting fittings, etc., and motive flow devices suchas pumps, compressors, impellers, ejectors, eductors, etc., for flowingwastewater into and out of the electrolytic oxidation cell.

Preferably the non-electrically-conductive, liquid-permeable barriercomprises a plastic netting, but other permeable barrier structures maybe employed, such as mesh, screen, membrane or other structures of aliquid permeable and non-conductive character, as hereinafter more fullydescribed.

The iron chips are preferably generally disk-shaped, but may be of anysuitable shape and size characteristics.

An electrolytic oxidation apparatus according to the invention mayfurther comprise one or more additional electrolytic oxidation cellssimilar to the first, with means such as pump and conduit elements toflow the wastewater from the first electrolytic oxidation cell to theone or more additional electrolytic oxidation cells for sequentialpassage through the electrolytic cells in the apparatus system.

Various other aspects, features and illustrative embodiments of theinvention will be more fully apparent from the ensuing disclosure andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic top view of an electrolytic oxidation cellaccording to the invention.

FIG. 2 is a schematic representation of an electrolytic oxidationwastewater treatment apparatus according to one embodiment of theinvention.

FIG. 3 is a schematic representation of an electrolytic oxidationwastewater treatment apparatus according to another embodiment of theinvention, employing two electrolytic oxidation cells in series.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The present invention relates to an electrolytic purification apparatusand method for treatment of wastewaters to reduce chemical oxygendemand, by oxidation of water-soluble organic and other oxidizablematerials in one or more electrochemical cells. The desiredelectro-oxidation is conducted in one or more electrolytic oxidationcells that employ stainless steel electrodes and contain metal chips.The metal chips are mobile and circulate freely as liquid flows throughthe cell, so that the metal chips form many, ever-changing electricalcontacts with the anode, but are prevented from making electricalcontact with the cathode by a non-electrically-conductive butliquid-permeable barrier.

The metal chips thus provide a dynamic and fluid electrode surface thatis efficient and resistant to performance degradation. The wastewatermay be recirculated through the electrolytic oxidation cell(s) foradditional purification. The apparatus may optionally include monitoringdevices such as oxygen, pH, and/or conductivity meters, or means tosample the wastewater stream for parameters such as COD.

The electrolytic oxidation cells can be of any suitable shape andvolume, as may be readily determined based on the specificwastewater-generating process and/or wastewater stream characteristicsinvolved in a particular end use application of the invention. The cellis fabricated of any suitable material, as is readily determinable bythose of ordinary skill in the art without undue experimentation,preferably a material that is strongly resistant to degradation andrupture under the conditions of use.

In one illustrative embodiment, the cell is a non-conductive tubularcontainer with an inside diameter of from about 1 to about 3 inches anda length of from about 1 and about 3 feet. At the top of the tube, aflange is secured to the tubular container. The flange has threeopenings. Through two openings pass stainless steel rods which serve asthe electrodes, with diameters of about 1 mm each and a distance ofabout 10 mm therebetween throughout their length. The third opening inthe upper flange is an outlet for the treated liquid. At the bottom ofthe tube is an opening through which untreated solution is flowed intothe cell.

The stainless steel electrodes are fabricated with any suitabledimensions proportionate to the size of the electrolytic cellcompartment. The electrodes are formed of stainless steel. The stainlesssteel may be of any suitable type, e.g., 316 stainless steel alloy orany other advantageous stainless steel composition, as will be readilydeterminable by those of ordinary skill in the art.

The metal chips are formed of iron. The “chips” may be of any shape thatis conducive to free circulation and mixing in a flowing liquid streamand is not prone to clumping or adhesion to the electrolytic cell wallor electrode surface. In one embodiment the metal chips are generallydisk-shaped. Suitable dimensions for such metal chips may be readilydetermined without undue experimentation by those of ordinary skill inthe art. One highly preferred size of such metal chips is about 3 mm indiameter and about 1 mm in thickness. Other shapes of chips that may beusefully employed in the broad practice of the invention include flakes,rings, pellet shapes, spheres, cylindrical shapes, etc. Preferably, thechips are flattened or planar to enhance electrical contacting in theslurry of chips in the wastewater undergoing treatment. The chips may beof a single dimensional size, or the chips may constitute a populationof differing sized members, as may be desired or appropriate in a givenend use application of the invention.

The cell compartment is filled with metal chips to a level that allowsthe chips to mix and circulate freely in a flowing liquid stream, butthat is sufficiently concentrated in chips so that they will be infrequent physical and electrical contact with one another and with theanode. Desirably, the chips are able to mix and circulate freely andform many constantly changing current pathways, to provide a dynamic andfluid electrode surface. The cell is functional when filled in thevolumetric range of from about 20% up to in the vicinity of 100% withmetal chips, based on the volume of the cell chamber. The preferredfilling range is from about 80% to about 95% by volume, based on thetotal volume of the cell chamber.

A non-electrically-conductive but liquid-permeable barrier prevents themetal chips from making electrical contact with the cathode. Thisbarrier must be sufficiently liquid-permeable that the wastewater beingtreated can flow freely through the cell and between the anode andcathode vicinities. The barrier will preferably have openings or poreswhich may be regular or irregular in shape, and will have mean diametersof a size that will allow maximal liquid flow while preventing thethrough-passage of a deleterious, i.e. short-circuit-causing, amount ofthe metal chips during the operation of the electrolytic cell. Thepreferred dimensions of the openings or pores will be determined basedon the size of the metal chips being used.

The non-conductive but liquid-permeable barrier most preferably isformed of a material which is resilient to the constant impacts of themetal chips when the cell is in operation, which is chemically inertunder the conditions of electrolytic oxidation, and which is notelectrically conductive. Examples of suitable barrier materials includeplastic netting, polymeric films (e.g., of polyvinylidene chloride,polysulfone, polyvinylchloride, etc.), ceramic screens, sintered glassfiber sheeting, etc.

The wastewater to be purified in the practice of the invention mayrequire pretreatment to remove suspended solids, to adjust pH, and/or toadjust conductivity, prior to its introduction into the electrolyticoxidation cell. Accordingly, the process system may comprise an upstreamclarifier or sedimentation basin, screening unit, filter, chemicaldosing chamber, biological oxygen demand (BOD) removal treatment unit,radiation treatment chamber, ozonation unit, or any other pretreatmentunit that will advantageously assist the processing of the wastewater ina manner that will, in combination with the COD treatment system of theinvention, produce a final effluent of the desired discharge quality.

For example, the upstream optional pretreatment of the wastewater mayinclude processing to lower the levels of suspended solids in thewastewater, including sedimentation and/or filtration, with or withoutflocculation of the wastewater.

When not in use, the electrolytic oxidation cell is stored charged witha solution with a conductivity of from about 500 to 2000 μS/cm. Thesolution can be a simple salt solution, e.g. NaCI.

Prior to electrolytic oxidation treatment, the conductivity of thewastewater is adjusted to a suitable level, e.g., in a range of fromabout 200 to about 2000 μS/cm. A preferred conductivity for treatablewastewaters is in the vicinity of about 1500 μS/cm. The conductivity canbe adjusted with any strong electrolyte, e.g., alkali and alkaline earthchlorides, bromides, iodides, nitrates, perchlorates, chlorates,bromates, and alkali metal sulfates. For reasons of cost and simplicity,NaCl is typically used to adjust conductivity to a level sufficient tosupport electrolysis.

Also, prior to electrolytic oxidation treatment, the pH of thewastewaters is suitably adjusted to a pH level of from about 7 to about10, preferably from about 8 to about 10. Any strong inorganic base canbe used, but for reasons of cost and simplicity, NaOH or Na₂CO₃ aretypically employed.

In electrolytic oxidation of wastewater to reduce COD, fairly complexorganic molecules are frequently oxidized all the way to CO₂. In suchelectrodestruction reactions, many bonds are broken and large molecularrearrangements occur. Such reactions are often much slower than simplesingle-electron-transfer reactions. The flow rate, temperature, currentdensity and electrode potential will all affect the rate at whichcomplete electrolytic oxidation of the oxidizable contents of awastewater stream can occur.

In one illustrative embodiment of the invention using an electrolyticcell having dimensions described hereinabove, a voltage of 1-20 V isapplied across the electrodes to generate a current of 2-15 A.Preferably, the applied voltage is about 10 V yielding a current ofabout 10 A. The wastewater stream is pumped into the cell at avolumetric flow rate of from about 0.5 to about 5.0 liters per minute(L/min), preferably from about 0.7 to about 3.0 L/min. The wastewatermay be recirculated through the cell for a given number of times, orthere may be a system to continually feed and draw off wastewater,calculated to allow a suitable average residence time in the cell toyield the desired reduction in COD.

The wastewater treatment system of the invention may utilize anysuitable flow circuitry means, including pumps, fans, impellers, etc.,arranged in the flow circuit including piping, conduits, fittings,sensors, monitors, controllers, etc., as necessary or desirable in agiven end use application of the invention to achieve a desired level ofCOD reduction in a specific wastewater being treated. The wastewater mayderive from any suitable source, such as for example an industrialmanufacturing or processing facility, mining operation, riparianstreams, power generation plants, etc.

The process of the invention may be carried out at any suitabletemperature level, and preferably is at or near ambient temperature,e.g., temperature in the range of from about 5 to about 40° C.

The residence time of the wastewater in the electrolytic cell may bewidely varied, depending on the type of wastewater involved and its CODcontent (amount of COD, and types of COD-constituting components), aswell as the equipment constraints of the system, the degree of CODremoval required, the dimensional characteristics of the electrolyticcell(s) in the system, the volumetric flow rate of the wastewater intothe treatment system, and the current density and other processconditions utilized in the treatment system.

The specific conformation of equipment and the operating conditions tobe employed may be readily empirically determined, by varying theprocess system variables of interest and determining the resulting CODremoval efficiency, to select the structural form and the processingparameters of the electrolytic treatment system in a specificembodiment.

The electrolytic treatment method of the invention may be carried out ina continuous, semi-continuous, or batch mode, depending on the specificsof the wastewater being treated. It may be desirable to utilize thesystem of the invention in combination with holding tanks, surgereservoirs or other storage facilities when the wastewater flow isintermittent or highly variable in character.

The electrolytic oxidation treatment method of the invention may furthercomprise passing the wastewater through additional electrolyticoxidation cells in a series arrangement, to obtain more rapid treatmentor higher final purities. The cells in series may be operated from oneor more current sources and may have one or more pumping means, asappropriate for the size and flowrates involved.

The apparatus and method of the invention are useful for treatingwastewaters with COD in the range of about 200 ppm to about 2000 ppm.After treatment according to the invention, the wastewaters typicallyshow COD readings that are reduced by more than 50%, preferably by morethan 80%, and even more preferably by more than 90%.

In the course of electrolytic oxidation, metal ions released from theelectrodes can be chelated by organic substances present in thewastewaters, resulting in flocculation. The purification system caninclude a means for separating the flocculate from the liquid phase.

The floc separation may be effected in a sedimentation tank or gravityclarifier, centrifuge, filter or other suitable separation means,optionally with addition of a coagulant or agglomerating agent to thefloc-containing wastewater, to effect consolidation and enhancedseparation of the floc particles from the wastewater.

Referring now to the drawings, FIG. 1 is a schematic top view of anelectrolysis cell 10 according to one embodiment of the invention. Thecell includes a chamber containing anode 1 and cathode 2 immersed inelectrolyte 6. The cell is filled to about 80%-95% by volume of itscapacity with metal chips 4, which are prevented from contacting cathode2 by a porous barrier 3 which is itself not electrically conductive. Theanode and cathode are supplied with current from current source 11 at apredetermined voltage.

FIG. 2 is a schematic side view of a purification apparatus employingthe electrolysis cell of FIG. 1. As in FIG. 1, the cell comprises achamber containing anode 1 and cathode 2 immersed in electrolyte 6. Thecell is filled to about 80%-95% of its capacity with metal chips 4,which are prevented from contacting cathode 2 by a porous barrier 3which is itself not electrically conductive. The anode and cathode aresupplied with current from current source 11 at a predetermined voltage.Wastewater is pumped by pump 7 from wastewater collection tank 8 viaconduits 12 and 13 to the electrolytic oxidation cell compartment 5.

As the wastewater flows through the cell compartment, the metal chips 4are constantly agitated and present a dynamic surface to the liquidphase. For purposes of maintaining such agitation, the cell chamber maycontain an impeller or a gas sparger to enhance the degree ofcirculation of the water/chips slurry in the cell chamber.Alternatively, the circulation rate of liquid through the cell may beinherently sufficient to maintain the desired degree of agitation orcirculation of the chips in the water/chips slurry.

When current is supplied to the anode 1 and cathode 2 from currentsource 11, oxidation reactions occur at the stainless steel anode 1 andat the surfaces of the metal chips 4, which are in electrical contactwith the anode. Organic and oxidizable inorganic substances in thewastewater are oxidized, and the treated wastewater flows to three-wayvalve 9, from which depending on the valve position, it may flow viaconduit 14 to a storage tank 16. and then via conduit 17 to discharge toa waterway or a treatment facility (not shown). Alternatively, thetreated wastewater may be returned via conduit 15, collection tank 8,and conduits 12 and 13 to thereby undergo additional oxidation cycles.

FIG. 3 is a schematic representation of an electrolytic oxidationwastewater treatment apparatus 30 according to another embodiment of theinvention, employing two electrolytic oxidation cells in series.Wastewater from collection tank 31 is pumped by pumps 32 and 33 throughthe apparatus. Wastewater flows through conduits 34 and 35 to firstelectrolytic oxidation cell compartment 36, where anode 37. and cathode38 are immersed in electrolyte 39. Anode 37 is in electrical contactwith metal chips 40, which fill the cell compartment 36 to about 80% to95% of its volumetric capacity, and which are prevented from contactingcathode 38 by a liquid-permeable barrier 41 which is not itselfelectrically conductive. Current source 42 provides current to the anode37 and cathode 38, whereby organic and oxidizable inorganic substancesin the wastewater are oxidized.

Upon exiting the first cell, the wastewater flows via conduit 43 tosecond electrolytic oxidation cell compartment 44, where the process isrepeated. Second anode 45 and second cathode 46 are immersed in secondelectrolyte 47, which may be the same as first electrolyte 39 or may bedifferent. Anode 45 is in electrical contact with metal chips 48, whichfill the cell compartment 44 to about 80% to 95% of its volumetriccapacity, and which are prevented from contacting cathode 45 by aliquid-permeable barrier 49 which is not itself electrically conductive.Current source 42 provides current to the anode 45 and cathode 46,whereby organic and oxidizable inorganic substances in the wastewaterare oxidized. Alternatively, anode 45 and cathode 46 may be connected toa second current source.

The wastewater then flows via conduit 59 to three way valve 50, fromwhich, depending on the valve position, the wastewater may flow viaconduit 51 to a storage tank 52 and then via conduit 53 to discharge toa waterway or a treatment facility (not shown), or alternatively, thetreated wastewater is returned via conduit 54, collection tank 31, andconduits 34 and 35 for additional oxidation cycles.

Electrolysis in such a cell reduces COD in typical wastewater byoxidizing to CO₂ the water-soluble organic and other oxidizablecontaminants of the wastewater. Typical purification levels are in therange of 80-90% reduction in COD for one pass through the electrolyticoxidation cell, and can exceed 95% COD removal for recirculationsystems, or in multi-cell wastewater treatment systems of the invention.

The features and advantages of the invention are more fully shown withreference to the following non-limiting examples.

EXAMPLE 1

Treatment of Wastewater from a Power Generation Station

Wastewater from a power generation station with a COD reading of 100 ppmwas treated in an electrolytic oxidation apparatus of a type as depictedin FIG. 2. The initial pH of the wastewater was 9.8 and its initialconductance was 1280 μS/cm. The wastewater was pumped through the cellat a rate of 1.2-2.6 liters/minute. The voltage was held at 6.0 V andcurrent was 12.5 A. After 5 minutes, the outlet stream was tested forCOD with a result of 20-40 ppm, corresponding to a COD reduction of 60%to 80% in the effluent discharge stream, relative to the influent streamCOD level.

EXAMPLE 2

Treatment of Wastewater from Printed Circuit Board Manufacture

Wastewater from printed circuit board manufacture with a COD reading of200 ppm was treated in an electrolytic oxidation apparatus of a type asdepicted in FIG. 3, employing two cells in a series arrangement. Theinitial pH of the wastewater was 9.8 and its initial conductance was1300 μS/cm. The solution was pumped through the cell at a rate of about1 liter/minute. In the first cell, the voltage was held at 6-8 V andcurrent was 9-12 A. In the second cell, the voltage was 10-12 V and thecurrent was 9-12 A. After passing through the two cells, the outletstream was tested for COD with a result of 20-50 ppm, corresponding to aCOD reduction level of 75% to 90% in the effluent discharge stream,relative to the influent stream COD level.

EXAMPLE 3

Treatment of Wastewater from Landfill Seepage

Wastewater which had seeped from a garbage dump landfill site with a CODreading of 250 ppm was treated in an electrolytic oxidation apparatus ofthe type as depicted in FIG. 2. The initial pH of the wastewater was 9.0and its initial conductance was 1580 μS/cm. The solution was pumpedthrough the cell at a rate of 1.2-4.0 liters/minute. The voltage washeld at 9-9.5 V and current was 4.0-5.0 A. After 5 minutes, the outletstream was tested for COD with a result of 20-50 ppm, which correspondsto a COD reduction of 80% to 92%.

While the invention has been described herein with reference to variousillustrative features, aspects and embodiments, it will be appreciatedthat the invention is susceptible of variations, modifications and otherembodiments, other than those specifically shown and described. Theinvention is therefore to be broadly interpreted and construed asincluding all such alternative variations, modifications and otherembodiments within its spirit and scope as hereinafter claimed.

What is claimed is:
 1. An electrolytic oxidation apparatus for purifyingwastewater by oxidation of water-soluble organic and oxidizableinorganic substances contained therein, said apparatus comprising: anelectrolytic oxidation cell, where the cell comprises a stainless steelanode and cathode and contains iron chips, said chips being inelectrical contact with the anode and prevented from making electricalcontact with the cathode by a non-electrically-conductive,liquid-permeable barrier; pre-oxidation means for adjusting conductivityof the wastewater to a range of from about 200 μS/cm to about 2000μS/cm; means for applying a voltage in a range of from about 1 V toabout 20 V across the stainless steel anode and cathode to produce acurrent in a range of from about 2 to 20 amperes in the electrolyticoxidation cell to effect electrolytic oxidation conditions therein whenthe cell contains wastewater; and means for flowing wastewater into andout of the electrolytic oxidation cell.
 2. The electrolytic oxidationapparatus of claim 1, wherein the non-electrically-conductive,liquid-permeable barrier comprises a plastic netting.
 3. Theelectrolytic oxidation apparatus of claim 1, further comprising meansfor recirculating wastewater through the electrolytic cell.
 4. Theelectrolytic oxidation apparatus of claim 1, wherein the electrolyticcell comprises a tubular housing of elongate character.
 5. Theelectrolytic oxidation apparatus of claim 1, further comprising apretreatment chamber upstream of the electrolytic cell.
 6. Theelectrolytic oxidation apparatus of claim 5, wherein said pretreatmentchamber comprises a solids-removal chamber.
 7. The electrolyticoxidation apparatus of claim 1, further comprising a post-treatmentchamber downstream of the electrolytic cell.
 8. The electrolyticoxidation apparatus of claim 1, further comprising at least oneadditional electrolytic cell, wherein the electrolytic cells arearranged in a series arrangement, for sequential flow of wastewatertherethrough to produce a final wastewater effluent of reduced CODcontent.
 9. The electrolytic oxidation apparatus of claim 1, wherein thepre-oxidation means adjusts the conductivity of the wastewater to about1500 μS/cm, and wherein the current in the electrolytic oxidation cellis in a range of from about 9 to 12 amperes.